Well here is my take.
First of all, I was really expecting that the new MBA will have a backlit keyboard. I actually changed my mind about buying one, but now that I carefully though about it, I realized the following:
1. In the airplane, there is a light on top of you specially made for you to read and type on your keyboard. So that's not an excuse.
2. When its really dark anywhere, whether in bed or elsewhere, and you cannot even see your keyboard keys, maybe you should think twice. Looking at a laptop screen when the surrounding is really dark will strain your eyes quite badly. Having or not having a backlit keyboard wont change a thing here.
3. Most people who use laptop or computers enough, dont even need to look at the keyboard. Some keys like the Function key, and so on might need you to look at them, etc, but most of the time people dont look at their keyboards.
4. The MBA is meant to be a portable machine, not your main machine. Dont expect it to be perfect, and dont expect it to have every single feature in the book, while still being one of the slimmest, the lightest, and coolest laptops around.
5. For Apple to integrate a backlit keyboard, they will probable have to change or update the Motherboard (for the connection to the keyboard for the LEDs), add a sensor into the LCD screen, etc, all things that would probably show up on a next revision due to all the hardware changes. Someone can open up a new MBA and confirm all this. So do you wanna wait 6 months+ for this feature? Not me.
6. One could still use that USB LED light that others suggested. So when the circumstances are really bad that you
really need to see your keyboard, well, you pull that little USB thing and plug it in. No biggie, and its light and small, so you can always keep it with your laptop bag/sleeve/etc.
7. If apple did not include it on this MBA, and the next MBA is to be thinner, then dont expect a backlit keyboard on the thinner one. Unless some kind of magic happens and they figure a way to do it that would not have been possible now. Am sure Apple had to go back and forth on this for a while before deciding not to include it. Its not like they enjoy punishing us for removing features you know?
Its a big bummer nonetheless, but one can live without it.
I welcome any comments.